Injection devices for setting and dispensing a single or multiple doses of a liquid medicament are as such well-known in the art. Generally, such devices have substantially a similar purpose as that of an ordinary syringe.
Injection devices, in particular pen-type injectors have to meet a number of user-specific requirements. For instance, with patient's suffering chronic diseases, such like diabetes, the patient may be physically infirm and may also have impaired vision. Suitable injection devices especially intended for home medication therefore need to be robust in construction and should be easy to use. Furthermore, manipulation and general handling of the device and its components should be intelligible and easy understandable. Moreover, a dose setting as well as a dose dispensing procedure must be easy to operate and has to be unambiguous.
Typically, such devices comprise a housing including in particular a cartridge holder, adapted to receive a cartridge at least partially filled with the medicament to be dispensed. Such devices further comprise a drive mechanism, usually having a displaceable piston rod which is adapted to operably engage with a piston of the cartridge. By means of the drive mechanism and its piston rod, the piston of the cartridge is displaceable in a distal direction or dispensing direction and may therefore expel a predefined amount of the medicament via a piercing assembly, which is to be releasably coupled with a distal end section of the housing of the injection device.
The medicament to be dispensed by the injection device is provided and contained in a multi-dose cartridge. Such cartridges typically comprise a vitreous barrel sealed in distal direction by means of a pierceable seal and being further sealed in proximal direction by the piston. With reusable injection devices an empty cartridge is replaceable by a new one. In contrast to that, injection devices of disposable type are to be discarded when the medicament in the cartridge has been dispensed or used-up.
Document EP 1 003 581 B1 discloses a drug delivery devices for selecting and dispensing a number of user variable doses of a medicament. This device includes a housing, a cartridge holder for retaining a cartridge containing the medicament, a piston rod displaceable relative to the cartridge holder and a dose setting mechanism.
For some applications it can be advantageous to limit the minimum medicament dose that can be delivered from a device as well as the maximum dose. This may, for example, ensure that only a therapeutically effective dose can be administered. Such a functionality may be particularly relevant to combinations of drugs, where a minimum quantity of the combined drug is required to ensure sufficient delivery of one element of the combination to be therapeutically effective, whilst allowing some variation of the dose, which may be important for the other element of the combination.
In some applications it may be advantageous to offer a device which allows delivery of only one fixed dose value but also permits a ‘priming’ operation to be undertaken before each dose is administered.
A further application could be for a therapy in which a range of discrete, non-sequential doses of a medication may be required. For example the range of doses may be needed to satisfy the therapeutic needs of different user groups, or to allow individual users to deliver a different dose at different times of the day e.g. in the morning or in the evening.
The present disclosure provides a drive mechanism for an injection device that provides a minimum dose function. The drive mechanism also provides a maximum dose function The drive mechanism allows for a priming of the device, so that a user is able to dial and to deliver a rather small volume of medication, typically 2 international units (IU), to check whether flow occurs correctly through a needle assembly releasably attachable to a distal dispensing end of the device.
Implementation of the desired minimum and/or maximum dose function should be achievable by only modifying a limited number of existing device components. It is a further aim to individually modify minimum and maximum dose values or dose sizes by only changing a single or only a few components of the device. Hence, the minimum and/or maximum dose function of the device or its drive mechanism should be configurable by interchanging only one or a few components of the device or its drive mechanism. It is a further aim, that the improved drive mechanism is universally applicable to a large variety of drive mechanisms and injection devices. In particular, the improved drive mechanism should be equally applicable to disposable injection devices as well as to reusable injection devices.